How to create a persistent random countdown?

Question

Basically, I need a counter that will go backwards from 100-1 slowly as users enter our website. We are only giving out "100" free coupon but want to give the appearance that users are quickly grabbing them in order to create urgency and have the prospect give us their email. I am using Unbounce to host our mobile landing page.

I came across a similar post to mine but the code generated numbers randomly in the millions. Here is the link for further help: https://stackoverflow.com/a/17964971

Quick example:

Be the first to know when we launch! We are only giving out 100 coupons and there are only (x) amount left.

Click here to get yours!

Answer 1

Count down at a random rate between 5 seconds and 1 second, save the current to the browser so if the user revisits the page the number doesn't reset

(Demo)

var i = 100;
var counter = document.getElementById('counter');
if(localStorage.counter) {
    i = localStorage.counter;
}
function countDown() {
    if(i > 0) {
        i--;
        console.log(i);
        counter.innerText = i;
        localStorage.counter = i;
        var timeout = Math.floor(Math.random() * (5000 - 1000)) + 1000;
        setTimeout(function(){
            countDown();
        }, timeout);
    } else {
        document.getElementById('counter-wrp').innerText = 'Oh no, you missed out! All of the coupons are gone.'
    }
}
countDown();

<span id="counter-wrp">Be the first to know when we launch! We are only giving 
out 100 coupons and there are only <span id="counter" style="color: red;"></span> left</span>